(1) Field of the Invention
This invention relates to a solenoid control valve, and more particularly to a pilot-operated solenoid control valve for controlling a flow rate of refrigerant such that a differential pressure across the valve becomes equal to a differential pressure set by a solenoid.
(2) Description of the Related Art
A refrigeration cycle e.g. of an automotive air conditioning system is known which condenses or cools high-temperature and high-pressure gaseous refrigerant compressed by a compressor by a condenser or gas cooler, changes the condensed or cooled refrigerant into low-temperature and low-pressure refrigerant by a pressure-reducing device, evaporates the low-temperature refrigerant by an evaporator, separates the evaporated refrigerant into gas and liquid by an accumulator, and returns gaseous refrigerant obtained by the separation to the compressor. As the pressure-reducing device of the system, a pilot-operated solenoid control valve is used which is capable of controlling a flow rate of refrigerant by an electric current externally supplied.
The conventional pilot-operated solenoid control valve is comprised of a body containing a main valve and a pilot valve, and a solenoid for actuating the pilot valve. The solenoid is configured such that a shaft supporting a plunger is supported by two-point support at both ends thereof so as to prevent the plunger from sliding on the sleeve containing the same. To this end, bearings supporting the shaft are arranged on the same axis as that of the sleeve, and designed such that a clearance between the bearings and the shaft is small, with a view to prevention of the shaft from being inclined. A hysteresis characteristic exhibited when an electric current supplied to the solenoid is increased and decreased is reduced by the above configuration.
On the other hand, the pilot valve arranged in the body includes, for instance, a ball-shaped pilot valve element. This pilot valve element is held on an end of the shaft supported by the body in a manner movable forward and backward. The driving force of the solenoid is transmitted to the pilot valve element via the shaft of the solenoid and the shaft of the pilot valve.
Here, in the above solenoid control valve, to transmit the driving force of the solenoid to the pilot valve element, two shafts are interposed between the solenoid and the pilot valve. This is for the following reason: On the solenoid side, to support the plunger in a manner movable forward and backward on the same axis as that of the sleeve, it is necessary to arrange two bearings on the same axis as that of the sleeve. Further, when the solenoid is joined to the body containing the main valve and the pilot valve, since the axis of the shaft of the solenoid and the axis of the shaft of the pilot valve are not accurately aligned with each other, the shaft is divided for absorbing the misalignment of the respective axes of the shafts at the divided portions, so as to subsequently transmit the driving force of the solenoid to the pilot valve.
Further, in the conventional solenoid control valve, the assembly of component parts and adjustment thereof are carried out by using screws, and sealing thereof is effected by using rubber O rings. For instance, the solenoid and the body have fitting portions formed with screw threads, and they are joined to each other by screwing the solenoid into the body. Further, a set value for the solenoid control valve is adjusted by adjusting the load of a spring urging the main valve. This adjustment is normally carried out by adjusting the amount of screwing of an adjusting screw. Similarly, in the solenoid as well, the load of a spring urging the plunger in a direction away from a core is adjusted by adjusting the amount of screwing of an adjusting screw receiving one end of the spring.
In the conventional solenoid control valve, however, the solenoid is configured such that the hysteresis is reduced by its own configuration, and when the solenoid is screwed into the body, the shaft holding the pilot valve element is driven by the shaft of the solenoid. To realize the above construction, it is necessary to provide a portion for receiving the bearing for supporting one end of the shaft of the solenoid, and portions of the solenoid and the body via which the solenoid screwed into the body to connect them. Further, to transmit the force of the solenoid to the pilot valve element, it is necessary to provide two shafts. Thus, an increased number of component parts is required, which increases the manufacturing costs of the solenoid control valve.
Further, the portions of the solenoid and the body via which they are joined, and portions of the body and the solenoid in which adjusting screws for adjusting the loads of the springs are inserted require machining of screws, which hinders reduction of the manufacturing costs of the solenoid control valve.
Further, although the above joining portions are sealed by rubber O rings, it is known that refrigerant permeates the rubber O rings to leak outside the sealed portions depending on the refrigerant used. Therefore, there is a demand for minimizing the use of rubber O rings for sealing.